The composition, heterogeneity, and spacial arrangement of histone proteins in isolated S12 chromatin particles will be studied to gain information on eukaryotic chromosome structure: 1. Reproducible techniques to isolate S12 chromatin particles from calf thymus and mouse P815 tissue culture cells will be established based on micrococcal nuclease fragmentation and agarose gel filtration. 2. The chemical compositions, histone species composition, and DNA size of the above particles will be determined. Stoichiometry of various histone species in particles will then be estimated. 3. The above particles will be characterized with respect to buoyant density and size, and variations in histone content within these parameters using isopycnic and velocity centrifugation. 4. The spacial arrangement of histones in particles will be determined by bifunctional reagent mapping studies using disc electrophoresis. Controls on protein exchange and particle-particle cross-linking will be performed. 5. The fine structure of histone folding and neighboring in particles will be studied by isolating dimers, extensively digesting them with proteases, isolating peptides that were previously cross-linked, and determining their amino acid sequence.